1. Field of the Invention
The present invention relates to magnetic fields and levitation and more particularly to a method and apparatus for levitating objects using a magnet attached to the object to principally lift an object toward a core element of an electromagnet while driving the electromagnet with a variable duty cycle and frequency power source to fine tune the levitation forces. The invention further relates to a method of detecting magnetic field strength and variations therein between the core of an electromagnet and an adjacently suspended permanent magnet.
2. Background of the Related Art
The ability to levitate objects in a magnetic field is considered to be useful for many applications. One obvious application is in the area of model displays and toys. Levitation is very useful for adding a sense of realism and accuracy as part of suspending many models, such as those of satellites, aircraft, spacecraft, and the like, in mid-air. It is also desirable to be able to suspend some objects that comprise an artistic formation or work in mid-air. At the same time, however, levitation has beneficial applications for scientific work such as where isolation of a chemical or material both electrically and physically from its surroundings is desired. It may also be desirable to use magnetic levitation to suspend some materials during processing or storage to counterbalance some of the forces of gravity or to better control material positioning in low gravity environments.
In the past, several attempts have been made to provide methods or apparatus for levitating objects. Generally, such apparatus comprises one or more electromagnets, although permanent magnets have been used in some configurations, powered by an adjustable strength current source. The electromagnets are suspended above, or below, an object to be levitated and generate magnetic fields which are used to attract metal in the object, or repel permanent magnets mounted on the object. The electrical current supplied to the electromagnets is adjusted to vary the strength of the magnetic field established by the electromagnet so as to just counter the force exerted by gravity on a suspended object.
One major problem in previous levitation apparatus was to sufficiently or properly balance magnetic attraction, or repulsion, against gravitational forces on a levitated object to achieve levitation. That is, the object must be levitated with sufficient force to prevent releasing it to fall and, at the same time, without attracting it so strongly as to cause it to contact the magnet or surrounding structure. This is accomplished using a combination of sensors to detect the magnetic field strength, and feedback control over the electromagnets based on the sensor data. However, previous attempts at such controls have produced complicated, generally expensive, control circuits which operate unsatisfactorily in many applications. The sensors require very precise or critical alignment which precludes many commercial applications. Transient lateral motion or wobble of the object also causes severe problems for the feedback controls typically resulting in loss of levitation.
What is needed is a method and apparatus for levitating objects that has less stringent construction requirements or operational limitations and is low in complexity.